This invention relates to semiconductor components with at least one highly-doped diode, in particular with a Zener diode or a tunnel diode and at least one Schottky diode connected to it in parallel, having a low-doped epitaxial layer of the same type of doping on a highly-doped substrate of the first type of doping, with a zone of a second type of doping being diffused into the epitaxial layer and with a Schottky junction being formed between the epitaxial layer and a Schottky metal on the side of the epitaxial layer facing away from the substrate. In addition, this invention relates to methods of manufacturing such semiconductor components.
Zener diodes of the usual design have a high power loss because of the comparatively high voltage drop in the direction of flow. With so-called double Zener diodes implemented in the form of antiparallel pn junctions, the forward voltage of the other diode is added to the Zener voltage of the one diode. The forward voltage is subject to greater process fluctuations because of the bulk resistance, so that corresponding manufacturing tolerances also occur accordingly.
Japanese published patent application (kokai) JP 8-107 222 A describes a semiconductor component with a Zener diode, having a low-doped epitaxial layer of the same type of doping (N-) on a highly-doped substrate of a first type of doping (N+), with a zone of a second type of doping (P) being diffused into the epitaxial layer, and with a Schottky junction being formed between the epitaxial layer and a Schottky metal on the side of the epitaxial layer facing the substrate.
The layer structure of this semiconductor component is comparatively complicated, and accordingly, many diffusion processes and lithography steps are required, making manufacture of such components expensive. Thus, two metallizations are required for the Schottky junction and the Zener junction. In addition, guard rings around the Schottky junction must be produced in separate steps. Due to the position of the Zener junction within the epitaxial layer and the outer terminal contacting the substrate, the diode current flows through the epitaxial layer, which is a comparatively poor conductor, so there is an increased differential Zener resistance.
Japanese published patent application (kokai) JP 62-165 978 A describes a semiconductor component having a diffused area on a substrate with a Schottky junction there. Opposite types of conduction and double-diffused areas are arranged on the periphery of the Schottky electrode, and an ohmic electrode is provided in the outer area. A Zener diode is formed by the double-diffused areas. This design yields, on the one hand, a Schottky diode having a very short switching time and, on the other hand, a Zener diode connected in parallel, its Zener voltage being of a size such that the Schottky diode, which is sensitive to overvoltage in the reverse direction, is protected from voltage peaks.
The Zener junction formed by the double-diffused areas extends approximately at a right angle to the top side of the arrangement. Therefore, the diffusion concentration decreases uniformly for both areas from the surface toward the inside. Due to this concentration gradient, only a very narrow area near the surface is effective for the Zener junction, so that the Zener diode has only a very low current carrying capacity. Due to the asymmetrical layer arrangement, two photo-lithography steps are required, thus increasing the cost. In addition, two terminals are arranged side by side, resulting in a poor utilization of space by the semiconductor arrangement.